Ultra-Wideband (UWB) is a term for a classification of signals that occupy a substantial bandwidth relative to their centre frequencies (for example, according to the Federal Communications Commission (FCC) Rules, UWB signal is a signal whose fractional bandwidth (the ratio between its bandwidth to its center frequency) is equal or greater than 0.2 or its bandwidth is equal or greater than 500 MHz.). Their very high bandwidth allows UWB based radar systems to obtain more information about targets, and males it possible to build radar with better spatial resolution compared to conventional radar. Therefore the UWB radar devices are widely implemented for radar-based imaging systems, including ground penetrating radars, wall and through-wall radars, surveillance and medical imaging devices, etc.
For most radar systems, the received signal SNR (signal to noise ratio) is a crucial factor, which determines the detection/imaging performance. A well known approach for improving detection capabilities is to perform coherent integration. In this approach, the received signal is summed up repeatedly (on different transmit/receive cycles), and, as a result, the deterministic (repetitive) part on the signal builds up much faster compared to the noise, thus improving signal SNR; the longer the integration lasts, the larger the SNR improvement.
This problem has been recognized in prior art and various systems have been developed to provide a solution, for example:
U.S. Pat. No. 5,132,688 (Shima et al.) entitled “Pulsed Doppler radar system having an improved detection probability” discloses a pulsed Doppler radar system having an improved detection probability, comprising an antenna unit, a transmitter for transmitting a signal through the antenna unit, a receiver for receiving a signal reflected by a target through the antenna unit to provide a reception signal. A processing unit which receives the reception signal from the receiver determines, in accordance with a range of the target and a signal-to-noise ratio and bandwidth of the reception signal, an optimum integration number which maximizes the detection probability and performs coherent integration on the reception signal by the number of times equal to the determined optimum integration number thereby outputting a signal having a predetermined level. Such a signal is fed to a display and an image of the target can be viewed on a display.
U.S. Pat. No. 5,457,462 (Mitsumoto et al.) entitled “Radar signal processor and pulse Doppler radar system therewith” discloses a radar signal processor for use in a pulse radar system. Reception signals are given from a range divide and output circuit to a plurality of integration point variable coherent integrators, each of which is allocated to a different range domain. The range domain is given to an integration point setting section provided corresponding to each integration point variable coherent integrator. The integration point setting section determines the number of coherent integration points based on the given range domain and sets it in the corresponding integration point variable coherent integrator. The signal resulting from coherent integration by the integration point variable coherent integrator is discriminated to frequencies, and then supplied to any square detector for square detection for each frequency component. Square detection output is fed into a CFAR detector, which then makes its false alarm rate constant for a supply to a display, etc.